The central dynamic of global politics since September 11 2001 has been the profound shift in the nature of American foreign policy. After the end of the second world war, the United States emerged as the dominant world power, and yet, because of the cold war rivalry with the Soviet Union, its hegemony was exercised in an organic alliance, most notably with western Europe, giving rise to the notion, in its contemporary form, of "the west".

Despite its overwhelming dominance, the power, interest and identity of the US were partly subsumed in the idea and reality of the west, and "multilateralism" was a way of describing the symbiotic nature of the alliance. As Mary Kaldor points out, the cold war gave rise to the politics of the blocs, and the partial eclipse of the nation-state.

After the end of the cold war, there followed what now seems nothing more than an interregnum before the beginning of another defining epoch, the emergence of the US as the global hyperpower, freed from the Soviet threat, unconstrained by any alliance, able to explore and define its own interests unfettered and uncluttered by other considerations. Yet during this interregnum - the 1990s - it didn't appear like that. In the first Gulf war, the US was at pains to construct a global alliance, its multilateralist instincts still predominant.

The post-cold war world was a novelty for everyone. This was the era of "the end of". It became fashionable to consign the past to the dustbin of history - ideology, left, right, socialism, capitalism, imperialism (hopelessly old-hat) and the rest - while the future seemed a cornucopia of possibilities. In a world without constraint, finally freed from the force of gravity, anything seemed doable: the 1990s gave birth to the third way, technological utopianism, the biggest speculative bubble in history, neutral, interest-free globalisation.

Ellen Meiksins Wood is guilty in her book of glossing over this interregnum and, even more extraordinarily, of paying scant regard to the cold war: American behaviour and motivation can, for her, be charted as a straight line from the emergence of the US as the world's dominant power in the 1940s to the Bush administration of today. In a book firmly rooted in the Marxist tradition, she is guilty of a rather schematic view of history; the details barely detain her.

For her, the behaviour of the US during the cold war, the interregnum and under the Bush administration is as one. She ignores the way the Soviet threat dominated American foreign policy and shaped its alliances during the cold war and then, after the collapse of the Soviet Union, the delay before American policy re-emerged in a transformed environment. All this is subordinated to "the underlying interests of imperial capital".

Yet, whatever its weaknesses, this is a timely book, a reminder that you cannot understand the present unless you understand the past, a powerful antidote to one of the afflictions of the interregnum, the belief that appearance is everything.

Meiksins Wood seeks to explain the nature and causation of empire. By exploring the character of successive empires - Greek, Roman, Chinese, Spanish, Arab Muslim, Venetian, Dutch and British - she demonstrates the novelty of each imperial exercise, and in so doing reminds us both that empire is not coterminous with the classic age of imperialism a century or so ago, and that it doesn't necessarily involve the permanent acquisition of territory.

Ultimately, her object is to understand the novelty and specificity of the new American empire which she sees as essentially - and uniquely - an economic empire. The Bretton Woods agreement, Gatt and the establishment of the IMF and World Bank combined to give it institutional shape and expression.

The classic entity of the new American empire is the sovereign nation-state, rather than the colony. Other commentators on globalisation have argued that the nation-state is in decline; Meiksins Wood argues that on the contrary "the world today is more than ever a world of nation-states": "The very essence of globalisation is a global economy administered by a global system of multiple states and local sovereignties, structured in a complex relation of domination and subordination."

The most novel aspect of her argument concerns the present. She asks why it is that although, for the first time in the history of the modern nation-state, the world's major powers are not engaged in direct geopolitical and military rivalry, but solely in economic rivalry, "the United States has striven to become the most overwhelmingly dominant military power the world has ever seen." The presiding asymmetry of the present era, she writes, is not that between the United States and "rogue states", but between American military strength and that of all other major powers.

She argues, as does Michael Ignatieff, that, in contrast to a war against a nation-state, a war against terrorism is, by definition, unwinnable. But, far from being a military absurdity, for Meiksins Wood this is precisely its point. The new American doctrine is based on war without end.

Overwhelming military dominance is designed to discourage and intimidate the three main threats to American global supremacy: failed states, rogue states and the other major powers - China, Russia, Japan and the European Union. In the longer run it is the EU and - especially - China that are seen as the greatest danger to America's position.

At the same time, American military might is designed to discipline and intimidate all nation-states, fundamental as the latter are to the global system: "This war without end in purpose or time belongs to an endless empire without boundaries or even territory."

After the end of the cold war and the demise of the left as a global force, there was a widespread willingness to rethink attitudes towards America. The idea of the US as a global policeman, which now took root, was not simply an acceptance of the inevitable.

The arrival in the White House of Bill Clinton, who talked the language of human rights, gave it further credence and that was followed by the war in the Balkans, the re-emergence of ethnic cleansing in Europe, the abject failure of the EU to act, and then the decisive intervention of the US. In a world of one superpower, the mission of the US could in one reading be seen as intervention on the side of human rights and democracy. So was born the modern version of liberal imperialism.

Michael Ignatieff belongs to the liberal imperialist school of thought. He believes that the only way failed states can be saved from themselves is by American intervention. Unlike some liberal imperialists, whose rhetoric has become wilder and wilder as history has become less and less sympathetic to their case, Ignatieff's tone is always measured, his argument intelligent, his willingness to recognise its downside apparent. He does not pretend that American foreign policy belongs to a world of morality and high-mindedness: it is determined by realpolitik, self-interest and imperial ambition. Indeed, he declares that all these various adventures - Bosnia and Kosovo as much as Afghanistan - are part of America's imperial project.

He accepts that Bosnia remains in a mess, with no end in sight; he admits that Kosovo has swapped one kind of ethnic cleansing for another. He acknowledges that the Afghan puppet government is impoverished and never consulted. His chapters on each of these countries - written engagingly with a reporter's eye - leaves the reader pessimistic as to whether anything positive will emerge from the American presence there.

But in his conclusion Ignatieff sticks tenaciously to his basic credo: "Nation-building seeks to reconcile imperial power and self-determination through the medium of an exit strategy" - "empire lite", as he likes to describe it. For Ignatieff, "the central paradox is that imperialism has become a precondition for democracy."

Although Ignatieff has no qualms about admitting the imperial intent of the United States, he never analyses the nature of the new American unilateralism. Indeed, he fails to understand its character:

In the old imperialism, the empire had a single capital, and its objectives were opposed to those of every other empire. In the new humanitarian empire, power is exercised as a condominium, with Washington in the lead, and London, Paris, Berlin and Tokyo following reluctantly behind.
The humanitarian empire is the new face of an old figure: the democratic free world, the Christian west.

In the immediate aftermath of September 11, even after the invasion of Afghanistan, it was plausible to argue this, but since the invasion of Iraq it has become unsustainable. For all Blair's supine support for the war, London seems to have zero leverage when it comes to pressing its concerns. Few would have predicted that the French and Germans would decline to support the invasion, let alone Russia and China.

This is an empire with only one capital: Ignatieff's multipolar empire is a mental hangover from the cold war western alliance. It has not stood the Iraqi test. And his statement that "an imperial invasion of Iraq that replaced a hostile tyrant with a friendly one would be unworthy of support" suggests that he might be - or ought to be - persuaded to rethink his position in the light of events in that country.

This failure to confront the nature of American unilateralism, common to all the liberal imperialists, leaves one with the impression that they have failed to grasp the big picture, preferring instead to gaze wistfully at a small corner of it.

Ignatieff is at his most breathtaking, however, in his sweeping dismissal of post-colonial states. "The movements of national liberation that swept through the African and Asian worlds in the 1950s, seeking emancipation from colonial rule, have now run their course and in many cases have failed to deliver on their promise to rule more fairly than the colonial oppressors of the past."

And later: "For every nationalist struggle that succeeds in giving its people self-determination and dignity, there are more that only deliver their people up to a self-immolating slaughter, terror, enforced partition and failure" (my italics).

These are extraordinary statements. Almost 40% of the world's population lives in east Asia, yet it is difficult to think of a single failed state in the region. The Americans like to describe North Korea as a rogue state, and Burma is certainly a nasty one, but in truth the nation-state in east Asia has been a huge success story: strong, inventive and dynamic. If you enlarge the frame to include south Asia, the picture may be less rosy but it is still largely positive.

The African experience, of course, is far more mixed, as is the Arab world, but there is no reason to believe that imperial adventures are going to put that right. Indeed, some of the greatest difficulties these countries have faced have been a direct result of the imperial legacy - artificial borders and imposed racial diversity, for example - to which Ignatieff makes no reference. The Middle East - the national borders, the role of Israel, the subjugation of the Palestinians - was, for reasons we know, largely a western creation.

It has become fashionable to argue that sovereignty should no longer be regarded as sacred, that human rights, even democracy, could, under certain circumstances, justify its subordination and breach. For the majority of nation-states, self-rule and sovereignty are a historical novelty, a product of the last half-century or so.

The United States now poses a serious threat to this sovereignty, in the form of shock and awe interventions, brief occupations and hasty exits. Ignatieff's sweeping dismissal of the achievement of post-colonial states serves both to reinforce a Western hubris easily dismissive of other cultures, and to justify imperialist adventurism on a scale far wider even than that used to threaten the "axis of evil".

The idea of global civil society, as Mary Kaldor and John Keane both suggest, also belongs to the 1990s. They argue that civil society is no longer confined to territorial borders - Kaldor refers to "the domestication of the international" - and seek to make sense of, and conceptualise, the growing importance of non-state activism and dialogue in global affairs.

Civil society has always been a rather elusive concept, used and defined in many different ways. Kaldor, for example, excludes the market and its institutions: Keane includes them. Perhaps the greatest single difficulty both face is steering a course between a descriptive and a normative definition of global civil society - between what is and what ought to be (or, perhaps, what they would like to be).

Neither satisfactorily resolves the problem, and there is a certain amount of wishful thinking in their respective versions of what constitutes global civil society. There is also the obvious difficulty posed by the migration of the idea to the global level, when there is neither a global polity nor a global state.

But these are very different books. Kaldor writes as an academic and an activist - as an "organic intellectual" of the peace movement, to use an older parlance - and this lends her arguments passion and commitment. Her book is strong exactly where Meiksins Wood's is weak: namely, in her discussion of the cold war, which is perceptive and illuminating, not least on the respective roles played by coercion and negotiation in western and communist societies. Her idea of global civil society is rooted in the peace and human rights movements in eastern and western Europe - and the dialogue between them - that began to flourish during the era of détente and which helped to pave the way for the 1989 revolutions.

Kaldor argues rightly that the novelty of these revolutions has not been properly acknowledged: they have largely been seen as derivative, even imitative, of western Europe. But another reason their originality has not been properly recognised is that there are two stories to be told: one is about the movements, the other is geopolitical - the role of the US in the defeat of communism.

The support given by the countries of central Europe to the US in its invasion of Iraq makes sense only when you recognise the prestige enjoyed by the Americans as a result of their role in the defeat of communism. This has been far more influential than the part played by the human rights movements in shaping the post-communist settlement.

Kaldor argues that the post-cold war moment offered a new kind of international possibility based on the emergence of a global civil society. At the heart of this possibility were the revolutions of 1989 and the new currents of international dialogue and exchange they enabled. Over a decade later, it does not feel like this.

In retrospect the new phenomenon seems more circumscribed, its reach limited in time and space. It largely belonged to western and eastern Europe - it was certainly international but manifestly not global.

The revolutions of 1989 transformed Europe and changed the dynamics of global politics by replacing a bipolar system with a unipolar order, but they did not come to define global politics in the way Kaldor hoped, partly because of the way they were hegemonised by the US and partly because they were primarily European events and the locus of global power has, since 1989, progressively shifted elsewhere, to the US and towards east Asia, now the world's second most powerful economic region. The importance of the European stage has declined measurably since the end of the cold war.

A striking feature of both Kaldor and Keane is their tendency to discuss global civil society largely in western terms. In fairness, Keane does make a limited attempt to embed his argument in other cultures, notably in Islam, but he barely mentions China. Kaldor's argument is overwhelmingly European (and also north American), with a nod in the direction of Latin America, token references to India and next to nothing on China.

And yet China is likely, within a decade or two, to become the next superpower. Either global civil society is an overwhelmingly western phenomenon, in which case it is not global at all, and has very limited utility, or it needs to be situated in a far wider context than either of these books provides.

The global space that is the object of Keane and Kaldor's concern is unquestionably growing in importance, though I am agnostic about whether "global civil society" is a suitable term to describe something that remains patchy, hugely western, contingent and often elusive.

Global civil society should not be seen, as it often is, in any simple opposition to the nation-state, whose significance and power ought not to be underestimated. For example, one of the most common fallacies is to believe that the WTO meeting in Seattle in 1999 failed because of the anti-globalisation protests. It did not. It failed because a wide swathe of developing countries - nation-states - were deeply dissatisfied with the Uruguay round and objected to the latest set of American and European demands.

Likewise, Cancún failed primarily because Brazil, South Africa, India and China banded together to resist western demands. The key source of opposition was not, as western hubris holds, the anti-globalisation movement of the developed world (though this made a contribution), but the nation-states of the developing world.

Kaldor is well aware that recent events have been unkind to her idea of global civil society. One of her admirable qualities is her honesty about her own hopes and dreams and her disappointment about the increasingly unfavourable turn of events: her book includes an excellent discussion of what she describes as the "NGOisation of public space" in the 1990s.

Tellingly, near the end she writes: "Will we look back on the last decade as the 'happy Nineties'? Was it an interregnum between global conflicts when utopian ideas like global civil society, human rights, a global rule of law, or global social justice seemed possible? Or was it, on another interpretation, the moment when global civil society came of age?" I fear the answer is already pretty clear.

· Martin Jacques, a visiting fellow at the LSE Asia Research Centre, is completing a study of east Asian modernities.

· To read more online essays from the current edition of the London Review of Books visit the LRB. The extensive online archive of essays from the past includes Alan Bennett's Diary and much more.